I have to admit, when the three 51-point Mage talents were revealed, Deep Freeze was the one I was least excited about. In its initial form, the spell was 1.5 second cast, 5 second duration stun that only worked on frozen targets. Ok.../golfclap. I shelved the spell in the dark recesses of my brain and devoted most of my time to pleasant fantasies involving Arcane Barrage, Living Bomb, and a lot of Gnomes.
Then a funny thing happened. Over several new beta builds, the spell actually became good. When I finally got into the beta and was able to take the spell for a test-drive, I discovered it was very good. Not perfect, mind you, but highly effective.
Damage was added to the spell. High damage. Then the cast time was removed, making it instant. The spellpower coefficient remained what it had been when it had a 1.5 second cast. All of a sudden, Deep Freeze was an instant-cast nuke with a reasonable cooldown that also delivered a stun mechanic. Suddenly, the spell had become...well, pretty awesome, actually.
So how does it work in practice?
Not too shabby at all, to be honest. It's no Mirror Image, but what is?
The Frost tree has always been about control and high burst-damage. Two of the basic mechanics a Frost Mage must master are learning how best to keep opponents frozen or slowed, and how to effectively deliver a Shatter combo when the time is right.
Deep Freeze helps with both of these mechanics. The damage output of the spell makes it an attractive option for use at the end of a Shatter combo, and because the five-second stun also acts as an additional freeze effect--one you can't break with damage--it's perfect to provide additional control. The spellpower coefficient is respectable, scaling like a 1.5 second cast, benefiting from 42.9% of your spellpower. The damage of this spell compares favorably with a Frost Mage's other primary nukes, Frostbolt and Ice Lance (on frozen targets), and its mana cost is reasonable, so it's absolutely worth using.
It's designed for PvP utility, and it certainly delivers that. It won't add much to raiding DPS, and so is limited in that respect. It's currently bugged so that the two-second stun of an Impact proc overwrites the 5 second stun of the Deep Freeze, even if Impact procs on the Deep Freeze cast itself. This will have to be fixed, and I expect it will be before the spell goes live. The stun also seems to share diminishing returns with other stuns and freezes, which may limit its usefulness in Mage-Rogue Arena comps.
In essence, what we have here, Frost Mages, is an instant-cast, 5 second CC that does rock-solid damage and allows you to make your Shatter combos significantly longer. You'll kill faster and live longer with it than you did without it. It isn't flashy, but it's effective. And anything that keeps that Warrior and his dual-wielded giant rotating pain-saws of death away from you a little longer (and preferably after he's already blown his trinket) is something I think we can all agree is a very, very welcome addition to our repertoire.